Background: Anaplasma ovis infections can cause clinical symptoms in acute phase and lead to huge economic losses in flocks. The aim of the present study was to investigate the hematological and parasitological changes in experimental anaplasmosis in sheep with Iranian strain of A. ovis. Method: Five male sheep without any blood parasite infection were selected. One hundred ml heparinized blood was collected from splenectomised sheep that showed 6% A. ovis parasitemia. Inoculums of 20 ml blood were administered intravenously to each test animal. Hematological, parasitological and clinical changes of experimental anaplasmosis were studied in 0-38 days post infection. Result: Parasitemia was detected 3 days post infection and reached its maximum level on the day 12 of experiment in test animals. Then the parasitemia was declined, but the organism could be found persistently until the last day of study. The red cell counts, packed cell volume and hemoglobin concentration were decreased and mean corpuscular volume was increased significantly during the infection period. Reticulocytosis and basophilic stippling were also detected. No significant changes were observed in total and differential leukocyte count and animal body temperature. Conclusion: Experimental A. ovis infection in sheep resulted in marked normocytic normochromic anemia at the beginning of the infection which became macrocytic normochromic by the development of the disease. There were negative correlations between parasitemia and RBC, PCV and Hb values, therefore hematological assessment can be considered as a practical diagnostic tool in ovine anaplasmosis.